I. Field of the Invention
This invention relates generally to munitions of war, and more particularly to the configuration of a standoff sensor antenna on the face on an explosively formed penetrator (EFP) whereby the munitions can be exploded upon reaching a predetermined standoff distance from the target.
II. Discussion of the Prior Art
Those skilled in the art recognize that certain anti-armor munitions employing EFP warheads, such as a Miznay-Shardin type of warhead, generally require five to six charge diameters of standoff distance from armor surfaces at the time of detonation to properly form the penetrating, molten metal jet used to defeat the armored target. Munitions with the EFP warhead are generally comprised of a cylindrical canister containing an explosive charge and a metal warhead secured to the end of the canister and especially formed to provide a forwardfacing concave surface. Groups of such munitions are commonly dropped from aircraft as a cluster and during their descent, small parachutes built into the munitions deploy to control the rate of spin and descent of the munitions toward the target or targets to be destroyed. These types of munitions can be deployed by artillery shells as well and would typically deploy a parachute or drogue chute for spin/speed stabilization.
To provide the desired standoff distance required for proper EFP formation, such munitions have been equipped with an elongated probe, typically exceeding two feet in length, and passing through the center of the warhead. When the tip of the probe touches a surface, such as armor plate or the ground, the charge is detonated and because the spacing provided by the probe configuration, the warhead can invert and liquify and form into a shape permitting penetration of armor plate. It has been found that the presence of such a probe significantly interferes with the formation of the penetrator, adversely affecting its armor piercing capabilities.
Standoff initiation of EFP warheads has also been accomplished utilizing electronic means. Specifically, radio frequency (RF) proximity sensors have been incorporated into Miznay-Shardin weaponry whereby the munitions is made to explode above the target surface or ground.
There are three known prior art standoff sensor antenna configurations which have been employed on submunitions. In a first arrangement, the concave face of the EFP is filled with a plastic foam to provide a flat, planar surface on which the antenna is disposed. This arrangement is used primarily for more expensive, target ranging and detection systems and is not particularly suitable for low-cost, short range EFP standoff. Because of the thickness of the foam layer, the conductive EFP cannot function as a ground plane for a microstrip antenna nor can the EFP be relied upon to provide radiation shaping of the antenna beam pattern.
In a second prior art arrangement, the proximity sensor and electronics associated therewith protrude through the apex of the conductive EFP and does not differ significantly from the probe arrangement previously discussed. That is to say, because the electronics and antenna protrude through the thickness dimension of the EFP, it will act to substantially degrade the performance of the EFP in that a significant portion of the whole EFP is missing.
In a third arrangement, a ring is provided around the base of the EFP allowing a ring dipole antenna and the RF sensor electronics configured in an annular shape around the circumference of the EFP base. While this configuration will not impact the EFP formation significantly, the configuration, for antenna purposes, is far from ideal. In that the dipole antenna must be bent around in a circular arch to fit the ring form, it will yield less than optimal antenna radiation patterns. Moreover, the ring approach requires more volume for packaging and would sustain the brunt of G-loading if used in a high setback (gun-fired) application, leading to questionable survivability.